Low frequency acoustic reverberation from highly porous seafloors under grazing incidence
conference paper
The European Defence Agency project RUMBLE-2 (ref.[1]) offered the opportunity for investigating
experimentally acoustic reverberation at about 1.kHz, under grazing incidence (less than about
20°), from very porous clayey seafloors of a continental shelf (mean grain size spanning from about
7 to 10 in units); the instrument was an operational, carefully calibrated LF towed triplet-array
sonar. Assuming Lambert law, observed values for the normal backscattering strength μ0 spanned
between –20 dB to –12 dB, i.e. 10-15 dB higher than usually recommended values for soft seabeds.
The objective of this article is to understand such high values of inverted μ0’s during the
RUMBLE2 experiments, which appear at first glance considerably high, particularly when
considering the nature of the sedimentary cover. As displayed by the map on the left of Figure 1,
the inverted μ0’s are ranging from about –20 to –12 dB, for a seabed covered by very thin clays with
Mean Grain Sizes of 8 to 10 units (porosities more than 85%), as shown by the chart on the right
of Figure 1. Usually recommended values for μ0 are 10 to 15 dB lower, or even more; we have to
explain such a disturbing discrepancy.
experimentally acoustic reverberation at about 1.kHz, under grazing incidence (less than about
20°), from very porous clayey seafloors of a continental shelf (mean grain size spanning from about
7 to 10 in units); the instrument was an operational, carefully calibrated LF towed triplet-array
sonar. Assuming Lambert law, observed values for the normal backscattering strength μ0 spanned
between –20 dB to –12 dB, i.e. 10-15 dB higher than usually recommended values for soft seabeds.
The objective of this article is to understand such high values of inverted μ0’s during the
RUMBLE2 experiments, which appear at first glance considerably high, particularly when
considering the nature of the sedimentary cover. As displayed by the map on the left of Figure 1,
the inverted μ0’s are ranging from about –20 to –12 dB, for a seabed covered by very thin clays with
Mean Grain Sizes of 8 to 10 units (porosities more than 85%), as shown by the chart on the right
of Figure 1. Usually recommended values for μ0 are 10 to 15 dB lower, or even more; we have to
explain such a disturbing discrepancy.
Topics
TNO Identifier
462561
Source title
Proceedings of the 11th European Conference on Underwater Acoustics - ECUA 2012, 2-6 July 2012, Edinburgh, UK
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